Method of forming subterranean barriers with molten wax

ABSTRACT

A method of permeating and infusing a formation around the borehole with wax by heating a formation surrounding a borehole and pumping molten wax into the formation, wherein the molten wax flows into and fills voids the formation without disrupting the formation is described. Also, a method of permeating and infusing a formation around the borehole with wax by heating a formation surrounding a borehole, pumping molten wax into the borehole, heating and circulating the molten wax vertically within the borehole for an extended period using a heater and pump attached to a circulation pipe extended to the bottom of a zone of the borehole to be heated, and recovering molten wax from the borehole by displacing it back to the surface with another material of different density is described. Additionally, a method of forming subterranean barriers by drilling multiple closely-spaced boreholes along a subterranean boundary, treating the boreholes with infusions of molten wax, and forming a hydraulic barrier along said boundary is described.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application is a §371 U.S. national stage filing of internationalapplication PCT/US2007/020064, filed Sep. 14, 2007, which was publishedin English on Mar. 20, 2008 as WO 2008/033536, and claims priority toU.S. Provisional Patent Application Ser. No. 60/844,432, which was filedon Sep. 14, 2006.

FIELD OF THE INVENTION

The present invention relates generally to a system and method for usingwax to seal both highly and marginally porous soil and rock materials ofsubterranean formations to create subterranean hydraulic barriers forthe protection of groundwater resources. The barriers may be used toprevent pollution due to coal bed, oil, tar sands, or oil shale recoveryoperations.

BACKGROUND OF THE INVENTION

In the production of oil shale by an in-situ heating process, multipleboreholes are placed in the ground and heat is applied for a period ofyears to convert the heavy oil or kerogen into lighter oil that willflow or be mobilized by water or steam to recovery boreholes.

One problem to be addressed is that after recovering the bulk of the oilthe residual mobilized hydrocarbon liquids can become free to move inthe subsurface and may contaminate groundwater. Barriers of clay andcement have been used to create subsurface barriers to groundwatermovement. However, clay and cement cannot permeate most soil or rock.Creating an effective barrier generally requires removal of soil androck material. This is a tedious task for depths over 100 feet. For oilshale recovery, the barriers may need to be up to a half mile deep.Placing the barriers is more difficult to control as depth increases.The barrier may need to extend through many formation layers ofpermeable and impermeable strata.

Freeze barrier of ice within the soil formation constructed by means ofrefrigeration pipes lowered into boreholes have also been used. Abarrier may be needed to facilitate removal of groundwater within theperimeter of the barrier to improve heat distribution and prevent themobilized hydrocarbon fluids and gas from migrating out of the heatedzone. However, a freeze barrier may be ineffective in formations that donot contain sufficient water to form a barrier at all locations, areimpermeable to water, or contain mostly hydrocarbons. A freeze barrieralso may not be maintained in perpetuity to prevent environmentalcontamination. Even after final sweeping of the produced zone with waterthere will still be residual hydrocarbons in the lower permeabilityareas of the strata that can contaminate groundwater if the freezebarrier is removed.

As described in U.S. Pat. No. 5,879,110, historically, jets have beenused to impinge upon and disrupt surrounding soil and insert wax andgrout in combination with a synthetic liner. U.S. Pat. No. 5,879,110 isincorporated by reference in its entirety. This disruption to thesurrounding soil is undesirable for large scale operations.

Thus, an impermeable subterranean barrier that is economical,environmentally sound, and effective is needed. An impermeablesubterranean barrier that is formed using a system that does not dependon the disruption of subterranean formations which may have variableproperties increases the reliability and potential depth range. Acontrolled and propagated permeation grouting in which the range ofpermeation of the grout is controlled by thermal pre-heating of theformation, rather than dictated by the local formation permeability,ease of disruption, or fracture properties is needed.

SUMMARY

In accordance with one embodiment, the present invention provides amethod of permeating and infusing a formation around a borehole with waxby heating a formation surrounding a borehole, pumping molten wax intothe formation, and allowing the molten wax to flow into, permeate andfills voids in the formation without disrupting the formation.

In accordance with another embodiment, the present invention provides amethod of permeating and infusing a formation around a borehole with waxby heating a formation surrounding a borehole, pumping molten wax intothe borehole, heating and circulating the molten wax vertically withinthe borehole for an extended period, and recovering molten wax from theborehole, suitably by displacing it back to the surface with anothermaterial of different density. In preferred embodiments, heating andcirculating the molten wax is achieved using a heater and pump attachedto a circulation pipe extended to the bottom of a zone of the boreholeto be heated.

In accordance with another embodiment, the present invention provides amethod of permeating and infusing a formation around a borehole with waxby heating a formation surrounding a borehole, drilling a plurality ofclosely-spaced boreholes along a subterranean boundary, pumping moltenwax into the boreholes, and allowing the molten wax to permeate into aformation surrounding the boreholes thereby forming a hydraulic barrieralong said boundary, or heating and circulating the molten waxvertically within the borehole for an extended period, and recoveringmolten wax from the borehole, suitably by displacing it back to thesurface with another material of different density. In preferredembodiments, heating and circulating the molten wax is achieved using aheater and pump attached to a circulation pipe extended to the bottom ofa zone of the borehole to be heated.

In accordance with another embodiment, the present invention provides amethod of forming subterranean barriers by drilling multipleclosely-spaced boreholes along a subterranean boundary; treating theboreholes with infusions of molten wax; and forming a hydraulic barrieralong said boundary.

In accordance with another embodiment, the present invention provides amethod of forming subterranean barriers by drilling multipleclosely-spaced boreholes along a subterranean boundary; treating theboreholes with infusions of molten wax; and forming a hydraulic barrieralong said boundary, or cutting a pathway between adjacent boreholeswith an abrasive cable saw, circulating molten wax through the pathwayto form a hydraulic barrier; and allowing the molten wax to permeateinto a formation surrounding the pathway and the pathway.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depicting an embodiment of a row of verticalboreholes drilled along a desired pathway of a vertical barrier in anunsaturated rock or soil formation.

FIG. 2 is a schematic depicting an embodiment of a row of verticalboreholes in a formation containing fractures with the natural watertable near the surface.

FIG. 3 is a schematic depicting an embodiment of a vertical barrierconstructed from a series of substantially horizontal directionallydrilled boreholes.

FIG. 4 is a schematic depicting an embodiment of a substantiallyhorizontal directionally drilled borehole with a wax permeated cutproceeding upward from it.

FIG. 5 is a schematic depicting an embodiment of a substantiallyhorizontal barrier constructed from a series of substantially horizontaldirectionally drilled boreholes.

FIG. 6 is a schematic depicting an embodiment of a variation of FIG. 4wherein the wax permeated cut proceeds downward between adjacentvertical holes.

FIG. 7 is a schematic depicting an embodiment of a method of circulatingmolten wax within a particular vertical interval of open borehole.

FIG. 8 is a schematic depicting an embodiment of a series of boreholeswherein water is being pumped from the bottom of every other borehole.

FIG. 9 is a schematic depicting an embodiment of a series of boreholeswherein the molten wax permeates radially outward through a heated zonewhich overlaps between the boreholes.

FIG. 10 is a schematic depicting an embodiment of multiple subterraneanperimeter barrier walls, laid out in hexagonal patterns.

FIG. 11 is a schematic depicting an embodiment of a method of applyingheated matter or molten wax to only a portion of a borehole or damagedconcrete pipe.

While the disclosed methods and apparatus are susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. The figures and written description are not intended to limitthe scope of the disclosed inventive concepts in any manner. Rather, thefigures and written description are provided to illustrate the disclosedinventive concepts to a person skilled in the art by reference toparticular embodiments.

DETAILED DESCRIPTION

The present invention utilizes the unique permeation properties ofmolten paraffin, crude petrolatum, and other low viscosity molten waxesto provide an underground, desirably impenetrable barrier for use in theoil field services, oil shale recovery, and nuclear power industries. Attemperatures approaching the boiling point of water these waxes have avery low viscosity. These waxes can permeate sand, clay, and mostsedimentary rocks. These waxes can permeate sand, clay and mostsedimentary rocks with a wicking action. Molten wax permeates clay andlow permeability sedimentary rocks by a capillary wicking action thatallows the wax to move through heated formations more readily than waterdoes. Molten wax can also penetrate micron size fractures in rock.Molten wax can pass between the microscopic laminations in competentshale rock but its movement stops when it reaches an unheated formation.In a formation heated significantly above the melting point of the wax,the molten wax remains low in viscosity and can flow a great distance.Molten was poured into a uniformly heated borehole moves into the heatedzone and forms a waterproof matrix within the heated radius, fillingporosity of the heated rock zone as a liquid fills a cup. Subterraneanbarrier walls may be formed by heating a row of holes such that theheated radius of each hole overlaps. By addition of surfactantadditives, wicking is enhanced and these molten waxes can betterpermeate materials with significant moisture content. With the properconditions, molten wax can be used to form a waterproof barrier in awater-wet formation.

By means of such methods, deep vertical barriers may be formed by waxpermeation between adjacent drilled boreholes that are preheated withheating systems or heated by circulation of molten wax or other fluids.Wax barriers do not require the removal of native material in thepathway but instead permeate the formation. Barriers can potentially beformed thousands of feet deep. Another advantage of the present methodsis that the excess water in the formation, i.e., formation water, may beextracted from the bottom of the boreholes used to form the barrier andmolten wax can flow through solid rock and seal fractures and voidsbetween holes that do not directly connect to the boreholes. Barriersmay be formed by wax permeation between at least two adjacentdirectionally drilled holes. Basin shaped, partially horizontal barriersmay thus be formed under contaminated lands by forming barriers betweena series of directionally drilled holes. Vertical barriers may also beformed between a pre-heated directionally drilled horizontal boreholeand the surface, along a sawed pathway that is heated by a flow ofmolten wax as it is being cut. Barriers may also be formed between twoadjacent substantially vertical boreholes along a sawed pathway that isalso heated by a flow of molten wax.

In this specification, “formation” means the strata of the earth, therock, or the soil of the earth. Holes drilled into a formation arereferred to as wells, boreholes, wellbores, or “holes.” Forming animpermeable subterranean pathway in a formation generally includesdrilling one or more boreholes along the desired pathway, heating atleast a portion of the formation through heating means or circulation ofhot matter into the borehole, and conveying molten wax into boreholessuch that it flows into the pores of a portion of the heated formation.

In the construction of impermeable barriers around a zone of oil shaleby previous methods, it is generally assumed that the barrier is a largesquare and that succeeding adjacent zones will also be contiguousadjoining squares of the same size. Such procedures can also be used inaccordance with the present invention. However, in addition to theimprovements obtained by making the barriers using molten wax, barriersin accordance with the present invention are desirably formed in ahexagonal pattern across the ground surface. For a square mile size areaenclosed by a barrier, using a hexagon shape with six equal sides 3276feet long compared to four sides 5280 feet long results in a perimeterthat is only 93 percent as long as the square area. The area perforatedwith heating wells to produce the oil must not be too close to thebarrier wall or the heat could compromise the wall. The barrier ispreferably more than 25 feet away from the nearest heating zone. Thehexagonal shape facilitates uniform heating better than squareenclosures and less acreage is left un-productive. Round enclosures arefine for mining a single area but are wasteful geometry if many suchenclosures are contiguous. Also the heat loss efficiency in the cornerareas will be improved, resulting in a significant energy savings.

Formation Preparation

In accordance with the present invention, there are several methods tobegin the construction of a subterranean barrier. Most methods begin bydrilling a row of vertical boreholes or wells along the perimeter wherethe wall is to be formed. A tracking instrument or inclination measuringtool may be used to monitor the verticality and/or position of theboreholes to keep them closely grouped and relatively parallel. Such“steering tool” instruments are known in the art of directionaldrilling. Vertical holes generally offer lowest cost but the holes mayalso be at an angle. These holes may be an open hole or cased near thesurface and cemented to the depth of the top of the barrier or to fulldepth. In various embodiments, it may be unnecessary for the barrier toextend back to the surface. The holes may be drilled using compressedair for cuttings removal or may be drilled with drilling mud. Then, themud may be displaced out of the hole with air, water, or molten waxbased fluids.

“Cable saw” means an abrasive wire rope, steel cable, diamond wire,chain, roller chain saw, or other abrasive tensile member that can forma cut through a formation. A pulley or sheave is a rollerfriction-reducing device for wire rope cable and is functionally thesame as a sprocket in the case of a roller chain saw in that it allowsthe cable saw to pass through an angle with greatly reduced friction.

The contact angle or “cable saw-to-formation contact angle” is thedegree of arc that the cable saw passes through while it is pressedagainst the formation. The total friction on a cable cutting through aformation is roughly described by the following relationship. The ratioof the tension on the pulling end of the cable to the drag on thetrailing end of the cable will be (T1/T2) T1/T2=eλα where λ is thecoefficient of friction and a is the angle of contact in radians. At 180degrees the angle is 3.141 radians and with a coefficient of friction ofapproximately 1.2, the friction ratio T1/T2 is about 43 to 1 such thatmost of the cutting power is lost to friction. If the weight of thecable is 1/43 the strength of the cable or the maximum winch pull, thecable will simply be stuck. Note that the formula applies to any shapearc from a gentle curve to a sharp edge. The actual coefficient offriction between the formation and the cable is quite variable so thelower the contact angle the more efficient the cutting process. Contactangles less than 180 degrees are most desirable for practicaloperations.

Excess ground water may also be removed prior to construction of a waxbarrier by placing extraction wells near the boreholes to be used forforming the wax barrier. If the rate of water movement through theformation is limited, it may be possible to pump water from the bottomof the same borehole that is used to form the wax barrier. The well maybe fitted with a screen and sand pack. The well may be used as an openhole to extract water from the formation and produce a drawdown conearound the well. This effectively dewaters the formation above where thebarrier is to be constructed. The bottom of the well and the drawdowncone potentiometric surface is preferably substantially below the bottomof the desired barrier. Molten wax is lighter than water and will floaton a layer of water. With multiple pipes in the borehole, the extractionof water may continue even while heating or wax permeation is inprogress. Another method is to simply heat the borehole with the waterin place and then pump molten wax into the borehole from the top andallow the wax to displace the water down the well and out into theformation or up a tubing.

It is difficult to make boreholes that are truly straight so a widerspacing tolerance increases the probability that the barrier will haveno gaps. Another way to apply the wax barrier method uses directionallydrilled holes to form the desired barrier. Directionally drilled holesmay be made at different depths to produce a stacked row of heatingpipes along the desired vertical pathway. Another technique is todirectionally drill angled pathway holes to the same depth and thenangle back to the surface, staggering the longitudinal spacing togenerate a grid of pipes along the desired pathway.

Directionally drilled holes with substantially uniform spacing may beinstalled to trace out a barrier in any orientation. Such barriers couldform a basin under a contaminated land area that threatens to pollutegroundwater. The basin structure could be formed in rock even if therock contained many small fractures because the wax would seal thefractures. Directionally drilled boreholes can be drilled to trace theshape of a basin under the contaminated area. A short surface casingcemented in place at each end of each hole can direct fluids into theborehole.

Construction of barriers in some other applications requires a higherdegree of certainty of the lack of gaps in the barrier. Accordingly, insome formations it may be desirable to mechanically cut a verticalpathway between more widely spaced adjacent holes to construct arelatively thin barrier along a long straight perimeter path. In thismethod the formation heating is accomplished by a flow of molten waxcirculated through the cut. This allows the molten wax to flow into theformation to create an impermeable formation on each side of the cut.This cutting method may be relatively expensive but it may require muchless wax since the barrier can be relatively thin if cut with a diamondwire saw or cable saw. This cutting can be done with a top-down methodor a bottom-up cutting action of a cable saw. The method uses a pulleyat each end of the path where the cable contacts the formation tominimize the contact angle of the cable with the formation. Formationcontact angles less than 180 degrees, and preferably less than 160degrees, are desirable for preventing generation of excessive frictionand sticking of the cutting cable.

FIG. 1 depicts a row of vertical boreholes 1, drilled along the desiredpathway of a vertical barrier in an unsaturated rock or soil formation.Heating means such as electric heaters 2, are inserted in the boreholesto heat the formation. The heating is continued until the heated zone 3,overlaps between adjacent boreholes. Molten wax 4, is introduced intothe borehole and allowed to permeate into the heated zone 5, around theboreholes. Additional molten wax is introduced into the borehole, slowlyfilling the porosity of the heated zone from bottom to top 6 or from topto bottom in the case of water saturated areas.

Larger fractures which do intersect with the borehole can require asignificant volume of costly wax to seal because the wax flows into themmore rapidly and may flow for some distance away from the heated zonebefore cooling enough to solidify. The rate of flow into the wellboreconnected fractures 58 can be reduced in certain embodiments bypre-grouting with cement or clay based grouts and drilling fluids whichplug the fractures connected to the borehole. The molten wax willpermeate and wick through the cement or clay grout at a relatively slowrate and enter these fractures. Due to the slow rate of flow, the waxwill rapidly cool and solidify at the point the fracture leaves theheated radius 59. Pre-grouting plus pre-heating of the boreholes resultsin minimizing the amount of grout and/or wax required while sealingfractures in the heated zone even if they do not connect with anyboreholes.

Thick deposits of oil shale may cover hundreds of continuous squaremiles so the land is desirably divided into manageable size areas thatcan share the same perimeter wall minimizing the length of the perimeterwall to be installed for the acreage mined.

The amount of wax required to produce a deep barrier around a largesection of land can be enormous. Thus tailoring the barrier to reducethe length of barrier needed is desirable. For example, if verticalholes are drilled on 8 foot centers around the field, then the wax mustpermeate to a distance of at least 4 feet from the wellbore to bridgethe gap between the drilled holes. Since holes generally are notperfectly straight, the actual diameter of the wax infused formationaround each borehole may need to be more like 5 or 10 feet. Thisprovides a minimum barrier thickness of 72 inches if the boreholes wereexactly 8 feet apart. If the boreholes were actually 9 feet apart, theminimum barrier thickness at the overlap would only be 52 inches. Theheating process to heat out to a 5 foot radius is relatively slow anddepends on may factors but is expected to take between 3 and 6 monthswith a borehole temperature of 400° F. and a rock formation temperatureof 80° F. The fractures and porosity of deep rock formations vary widelybut some oil shale formations also have significant porosity in the formof solution cavity holes. Wax is expensive compared to cement and claygrout materials. The amount of wax required to produce a barrier infractured and vugular rock formations can be reduced by pre-groutingwith other grout materials such as cement, flyash, lime, and mixtures ofcement and bentonite. When a formation has been pre-heated, the moltenwax has the capacity to slowly permeate through sedimentary rock as wellas any cured cement and bentonite grout plugs to access voids andfractures that do not intersect the borehole. The relatively slow rateof permeation into fractures and voids beyond the grout plugs helpsassure that the wax does not flow significantly beyond the heatedradius.

The entire vertical interval of a borehole may be pre-grouted by pumpingcement grout down a tremmy pipe to the bottom of the well and displacingthe grout to the top of the well, followed by displacing the excessgrout back into the tremmy pipe. The boreholes may be open hole all theway to the surface but are preferably equipped with at least a surfacecasing to provide for controlled circulation of the well. In someinstances, a surface of the borehole may be lined with artificialmaterial. Artificial material includes concrete, clay, or clay tile. Insome embodiments, the artificial material may be damaged and the waxpermeation may be used as a means of repair.

Temperature Tailoring

The distance the wax will permeate, or pass through micro-fractures, maybe increased by pre-heating the formation or using higher temperaturemolten wax or by pre-heating a larger radius around the borehole, byusing higher temperature or longer duration heating. The surface area tovolume ratio of the hole and fractures impact how rapidly the hot moltenwax will lose its heat to the colder formation. In accordance withvarious embodiments, the formation will first be heated prior to theintroduction of the molten wax. A heat source is applied to theboreholes within the zone where the barrier is to be formed to heat theformation to at least the melting point of the wax. Heat sources mayinclude resistance heaters, steam, hot water, hot oil, hot water, ormolten wax in a circulation pipe loop, hot air, microwave, or electricresistance or electric impedance heating. Others have demonstrated thatresistance heaters lowered into shallow wells can be successfully usedto heat a large block of soil. The same approach should work at greatdepths, though higher voltage may be required to transfer electric powermore efficiently. Hot air blower systems fired by combustion may be usedto circulate hot air through a pipe directly to the bottom of theborehole. The hot air then flows along the annulus between the pipe andthe open hole to the surface. Waste air may be re-circulated to theheater or used to pre-heat other boreholes.

The heaters may be operated for weeks or months until the soil formationis preferably at least hotter than the melting point of the wax.Optionally heaters may initially be placed in every other wellbore withtemperature probes in monitor wells between them to measure the initialtemperature profile of the heat from adjacent boreholes to help verifythat the entire pathway will be heated to at least some minimumtemperature. Thermal imaging tools lowered down the boreholes may beused to detect intervals that are not heating uniformly. Drilling theholes and heating the formation around a large section of land may takemany months. It may be schedule efficient to first drill the alternateholes that are to be heated first and begin the heating process in themas they are completed before drilling the monitor holes in between.After verifying that proper heating is occurring in the monitor wells,heating can begin in them as well. After the soil formation around aborehole has been at least partially heated, the heating process may becontinued using molten wax. Molten wax is introduced into the boreholesand a flow is maintained and recirculated molten wax is circulated inthe borehole while the wax permeates the formation and continues to addmore heat and expand the heated radius. After the soil formation hasbeen heated, molten wax is introduced into the boreholes and a flow ismaintained and hot wax is circulated in the borehole while the waxpermeates the formation. The molten wax is permitted to flow for anextended period of days or months until the wax has saturated thepre-heated zone. The cylindrical pre-heated zone will fill like a cupbecause the wax cannot flow substantially beyond the pre-heated zone,except where there are fractures and even fractures will self-seal atsome greater distance. The optimum hole spacing is an economic decisionbased on the cost of drilling, the cost of wax, and the cost of heatingto various radii around the borehole.

Alternatively, heating the borehole and surrounding formation isperformed by placing an electrical heating device into the borehole,placing a heat transfer fluid into the borehole, introducing heatedmatter directly into the borehole, introducing materials into theborehole to facilitate a chemical reaction that releases heat, orheating the drilling fluids used to drill the borehole.

Hot air can be circulated through the holes to pre-heat the formation.Other heating means such as electric heaters, heat transfer pipes,circulating steam or heated fluids, or introducing chemical reactantsthat release heat may also be used to heat the formation through andalong the boreholes. Circulating molten wax in the hole carriesadditional heat into the formation and increases penetration. Greaterpenetration of the wax allows wider spacing of boreholes. Pre-heatingthe formation surrounding the boreholes before introducing the moltenwax allows deeper penetration into the formation. The wax will permeatethrough and saturate at least the portions of the formation that areheated to the melting point of the wax. A deep subsurface barrier may becreated by heating the earth through multiple boreholes spaced atintervals such that the soil is heated to preferably at least above themelting point of the wax along the desired pathway. Heated matter, suchas water, air, or natural gas may be introduced into the boreholes toprovide heat to the formation between adjacent boreholes. Then moltenwax is introduced into the boreholes allowing the wax to permeate intothe heated area and cool.

Then, molten wax is introduced to the borehole, and desirably circulatedthrough the holes for an extended period, to allow formation of thebarrier. In embodiments where the molten wax is recirculated, the moltenwax is preferably re-heated and solids removed before recirculation. Thebarrier is formed by molten wax permeation outward from each hole to aradius sufficient to overlap or connect to the flow from the adjacenthole.

Having access to each end of the borehole limits the need for acirculation pipe in the hole, but it may still be used to help achievemore uniform temperature along the borehole or if there is no surfaceaccess to one or more sides of the contaminated site. In radioactivelycontaminated sites it may be preferable to perform substantially allheating before introducing the molten wax to prevent potentiallycontaminated wax circulating back to the surface.

Generally the native formation temperature is less than the meltingpoint of the wax for it to make a permanent barrier. The basic waxbarrier method described above may be improved by lowering a pipe to thebottom of the borehole and circulating molten wax between the pipe andthe hole. The wax is circulated back to the surface and continuallyreheated and the formation solids removed. Molten wax circulation may bemaintained for months to heat the formation around the borehole. Theradius of wax saturation will continue to increase as the molten waxcirculation continues, until a limiting distance is approached, due toself-insulation or thermal losses. Larger boreholes, higher molten waxtemperatures, lower melt points, and higher rates of circulation alltend to extend this distance. The solidified wax at the thermalinterface will tend to insulate the system. Accordingly, once heatinghas been started it is preferably continued until the desired permeationis complete. The wax can be pumped down the annulus and allowed to flowup the pipe, but it is preferred to pump the molten wax down the pipeand allow it to circulate back up the annulus because this provides themost even heating. If the borehole is relatively small the wax may coolbefore initial circulation is established. It may be desirable andpreferable to preheat the borehole, and thereby the formation, by a flowof hot air, hot water, or hot oil before beginning circulation of themolten wax. Faster circulation may also provide more even heating. Thecirculation pipe may be comprised of oil well tubing, casing or coiltubing. If only a portion of the borehole, such as an interval beginningat 1000 feet depth and extending to 1500 feet depth, requires a barrier,then an annular bridging device similar to a retrievable bridge plug maybe installed on the pipe at the 1000 foot depth and a second pipe, whichalso passes through the bridge plug, would be used to circulate themolten wax from the annulus back to the surface without filling theannulus above the bridge plug. The distance of wax permeation into theformation may be inferred from the total volume of wax accepted by eachborehole over time and core data indicating the porosity of each layerof strata. Additional boreholes may be drilled and cored between theinitial holes to evaluate and augment the barrier forming process.

If the strata varies greatly in permeability or fractures through thedepth of the desired barrier, some vertical segments of the barrier maybe created independently. The circulation heating method described abovemay be modified by drilling the hole to a limited depth and circulatingwax to form the barrier at that depth. After that segment is formed, theborehole may be drilled to a greater depth and the process repeated.Hydraulic fracturing may be selected to connect adjacent boreholes.Hydraulic fracturing uses or occurs when water or specially engineeredfluids are pumped at high pressure and rate into a region to be treated.Fractures occur along the lines of least principal stress, which aretypically vertical except very near the surface. By fracturing manyadjacent closely spaced holes at once it should be possible to createfractures following the line of holes. Perforating gun techniques may beused to created holes oriented along this line before fracturingoperation. Proppant, such as grains of sand, maybe mixed with the fluidto prevent closing of the fracture. Hydraulic fracturing providesimproved fluid transport within a large area of formation.

For a complex strata containing many impermeable strata zones, multiplepipes, and pipes extending only to desired strata may be used to produceextra heating in problem areas. Oil well cementing tools using slidingvalve mechanisms such as the Halliburton full-opening (FO)multiple-stage cementer may be used in conjunction with packer tools toselectively treat one or more vertical subterranean intervals withouttreating the rest of the borehole. Electric heating methods may also beused to preferentially produce more heat in one strata than another. Astrata containing more water may require much more heat input to reachthe desired temperature/radius profile around the borehole.

If groundwater present in some strata interfere with construction of thewax barrier, a freeze barrier may be constructed to dewater the workingarea before construction of the wax barrier. A freeze barrier is wellknown in prior art and can be constructed by drilling closely anduniformly spaced holes along the desired perimeter pathway and thenplacing a chilling means in the holes to remove heat over a period ofmonths. After a freeze barrier is constructed around the perimeter of anarea, additional wells in the interior may be used to extract theformation water. After the water is removed, a second row of holes isprepared inboard of the freeze barrier and a wax barrier may be formedin non-saturated conditions.

Wax Delivery

Boreholes drilled into the earth along the desired path of a barrier canbe filled with molten wax to seal existing fractures. The distance thewax penetrates away from the borehole will be limited by loss of heat tothe formation. Applying greater pressure to the wax will create or openthe existing fractures and allow deeper penetration, but the directionof travel will be uncontrolled. The wax will travel only until it coolsto a solid state. The most basic method of forming a wax barrier is tosimply pump hot molten wax into the boreholes. This can be effective infilling small fractures and cavities out a few feet from the borehole.This is particularly useful if the formation is substantiallyimpermeable but contains many fractures that cross the plane of thebarrier. It is most effective if the fractures are horizontal ratherthan vertical so that the chance of the borehole connecting with thefracture is maximized.

While vertical holes are preferred for making ultra deep verticalbarriers, it should also be possible to construct a vertical barrierusing horizontal directionally drilled holes. One method is to simplycreate a stack of roughly parallel and closely spaced boreholes alongthe desired path of the barrier. These boreholes are heated and thenmolten wax is circulated through the holes until the permeated zonesoverlap to form a continuous barrier. The bottom-up method works byfirst preparing a directionally drilled hole along the base of thedesired pathway. A wire rope cable is drawn into the underground pathwayalong with the pipe. This cable passes around a pulley sheave at eachend of the hole such that its total contact angle with the soil isminimized Friction increases dramatically with the angle of contact andcan result in the cable becoming stuck. Thus, the pulley positions aredesigned to reduce the degree of contact between the earth and thecutting cable. A flow of molten wax is initiated through the annulus ofthe hole with the wax being re-heated, filtered, and recycled throughthe hole. A pump at the receiving end of the hole collects the wax to berecycled.

A steel cable is tensioned and circulated through the hole in thedirection of the wax flow to generate friction, create a pumping action,and cut a pathway upward through the soil. A traction drive mechanismpulls an endless loop of cable preferably in the same directioncontinually, but the method could also be applied by reciprocating thecable back and forth. The pulley sheave positioned at each end of thehole may be fixed but may optionally be designed to gradually movetoward each other to produce a more uniform cutting force as the cableapproaches the surface. The wire rope cable is preferably a non-rotatingdesign that has large external wires that resist abrasion and act as apumping means.

A portion of the flow of molten wax will follow the rapidly circulatingcable moving preferentially through the upper portion of the cut wherethe cable is working. The molten wax transfers heat to the formationalong the pathway being cut. The wax quickly cools and solidifies in theareas of the cut no longer in contact with the hot circulating wax. Themolten wax permeates the formation along in the circulated areascreating an impermeable layer perhaps a foot into the soil on eitherside of the cut. Higher wax temperatures may be used to obtain deeperpermeation but temperatures below the boiling point of water arepreferred to avoid boiling due to formation water that becomes mixedwith the wax.

The bottom-up cut may be brought to the surface or stopped at a desireddepth. If the cable should break, the pipe in the bottom of the hole maybe heated to liquefy the surrounding wax and then used to pull a newpipe and cutting cable into the hole or a new cutting cable may beinserted or pumped into the hole, provided it has been kept molten bycontinued circulation. The cutting process then begins again from thebottom. The pipe in the directionally drilled hole may be withdrawn inthe same way after construction. Additional sides of the full perimeterbarrier can intersect the previous barrier partially melting it andcreating a seamless wall.

Another top-down method of mechanically cutting a pathway may be appliedto two or more adjacent substantially vertical boreholes. This method isthought to have more utility in hard rock formations. A number ofvertical holes are first created along the desired pathway. Two adjacentholes are heated as described above and filled with molten wax. Howeverin areas where the formation is unconsolidated, such as near thesurface, the holes may not be heated. This will minimize caving of thehole. Optionally, a small pipe may be placed to the bottom of thedrilled holes to circulate molten wax up the hole to maintain an openhole.

A pipe with a pulley sheave on its end is positioned over each of twoadjacent holes and a wire rope cutting cable or diamond wire cable isthreaded through the pulley sheaves. The pipes are lowered slightly intothe holes and the cable tensioned so that it bears on the ground betweenthe two holes on the surface. The ends of the pipes have multiplerollers that bear against the walls of the hole and minimize frictionwith the walls of the hole. A motive device, preferably a continuouscable traction drive, but alternately a pair of winches each alternatelypulling or paying out cable under tension, circulates the cable aroundthe pulleys creating an abrasive sawing action along a line between thetwo holes. Molten wax is pumped into a pipe in the first hole exitingfrom near the depth of the pulley such that the cable circulationcarries it toward the second hole. The first hole and its tubing has asealing means at the surface so that it can be pressurized. Cuttings areconveyed by the pumping action of the cable to the second hole.Optionally, a pipe extending to near the pulley of the second holedischarges molten wax at a lower pressure than the first pipe, such thatcirculation is established that carries these cuttings back to thesurface. The efficient circulation of cuttings may be enhanced bybubbles from an air jet, as is known in oil well drilling prior art.Heated air or other gas is injected below the point where the cable isdischarging cuttings into the second hole. The bubbles reduce the fluiddensity and help circulate the cuttings to the surface in the secondhole. The wax returning to the surface is continually cleaned ofcuttings by cyclonic devices and filters and it is reheated and recycledto the first hole. The pipes are allowed to descend into the holes asthe cable cuts a pathway between the adjacent holes. The downward forceon the pipes is continually adjusted in accordance with the cabletension to minimize the total contact angle where the cable contacts theformation. This minimizes total friction so that the cable does not getstuck. The heating action of the flow of molten wax heats the face ofthe cut and the molten wax permeates and wicks by capillary action intoeach side of the cut to form the barrier without any need to disrupt orfracture the formation. Higher wax temperatures may be used to obtaindeeper permeation.

The top down method may be applied with some modification to forming abarrier between two directionally drilled holes. Pushing pipes with endpulleys down into directionally drilled boreholes could be scheduled,but it is preferred to install the cable saw from the exit end of thetwo holes and pull pipes with pulleys on the ends to control the cablesaw-to-formation contact angle to less than 180 degrees and preferablyless than 160 degrees of arc. The cable may extend away from theformation contact area through the pipes back to the surface. Theinterior of the pipes may be coated with an anti-friction coating aswell as lubrication from the flow of molten wax.

A thinner permeation barrier may be formed in the top-down method bymechanically cutting a pathway between two adjacent boreholes with acable saw and will comprise at least the steps of;

-   -   1. Drilling at least two adjacent boreholes.    -   2. Placing an abrasive cable saw against the formation between        the two boreholes.    -   3. Continually positioning a pulley in each borehole to provide        a cable saw-to-formation contact angle of less than 180 degrees.    -   4. Circulating or reciprocating the cable saw to cut a pathway        through the formation.    -   5. Continuously circulating molten wax through the cut pathway        as the cut advances.

A thinner permeation barrier can also be formed by the bottom-up methodfrom a single directionally drilled hole and the surface or a shallowtrench by mechanically cutting a pathway between the hole and thesurface or trench comprising at least the steps of:

-   -   1. Directionally drilling a hole from the surface to depth and        then back to the surface.    -   2. Pulling at least one cable saw member or at least one cable        saw member and one pipe into the hole as the drill pipe is        withdrawn.    -   3. Fixing a pulley for the cable saw tangent with the hole at        each end such that a formation-to-cable contact angle of less        than 180 degrees is maintained.    -   4. Tensioning the cable saw around the tangent pulleys while the        cable is circulated or reciprocated through the cut.    -   5. Circulating molten wax through the hole in the direction of        cable saw travel such that at least a portion of the flow passes        through the pathway formed by the cut.

Both the bottom-up method and the top-down method may be modified toplace barriers made of other grouting materials such as mixtures ofhydrated bentonite and cement. The thickness of the barriers formed willbe limited to the thickness of the mechanical cut because thesematerials do not permeate significantly into most formations. Drying ofthe barrier materials or earth movement could cause failure. Molten tar,bitumen, or asphalt cement may also be a useful grout for thisapplication. It is not considered a wax by the present definition andwill offer little permeation but it may remain flexible and will not bedamaged by drying.

FIG. 2 depicts a similar row of vertical boreholes in a formationcontaining fractures 7, with the natural water table 8, nearer thesurface. A drill pipe or steel tubing 9, is inserted in the borehole andhot water or other fluid is circulated in the well to pre-heat theformation and fractures 10, out to some distance beyond the borehole 11.This can be performed as an independent step after drilling theboreholes. The circulation of hot fluid may also be done as the well isdrilled by heating the drilling fluids with a heater 12, tied into thedrilling mud circulation pump 13. In fractured formations, hot water maybe intentionally pumped into the fractures 14, to preferentially heatthe fractures out beyond the radius 15, of the heated zone around theborehole 16. Molten wax 17, is pumped into the annulus of the boreholeand displaces the water 18, or drilling mud downward causing the wateror drilling mud to flow back up the tubing 19, to the surface. Thepressurized column of molten wax 20, floats on top of the water columnand forces the water downward. The pressurized column of molten waxdisplaces the water radially outward 21 into the formation throughexisting fractures and the porosity of the rock. After the water ordrilling mud has been circulated out of the borehole, circulation isreversed and molten wax 22 is passed through a heater 23 and circulateddown the tubing and up the annulus under pressure to continue addingheat to the formation as the wax permeates even further 24 into theformation. As the heating and permeation continue, the columns ofwax-permeated rock grow together 25 and overlap as shown in crosssection plan view 26. After the interconnected columns form a completebarrier, the remaining molten wax in the borehole is displaced out ofthe well by circulating water down the tubing to force the molten wax upthe annulus to be recovered at the surface. This leaves the boreholefilled with water. Alternately, the molten wax or water may be displacedup the tubing by injecting air into the annulus, leaving the originalborehole clear and dry 27 so that it may be used to detect leaks in thebarrier.

FIG. 3 depicts a vertical barrier constructed from a series ofsubstantially horizontal directionally drilled boreholes that arestacked one above the other 28. After the horizontal holes are drilled,the boreholes are heated by a flow of hot material or by electricalmeans. Molten wax is then circulated under pressure through the holes topermeate the rock around each borehole to form a continuous verticalbarrier shown here in cross section view 29.

FIG. 4 depicts a substantially horizontal directionally drilledborehole. An abrasive cable 30 moves through the borehole 31, undertension and cuts a pathway upward toward the surface. The abrasive cableis driven by a traction drive or by movable winches 32. One or both ofthe winches may be moved to maintain an optimal cable-to-soil contactangle. A flow of molten wax passing through the hole carries cuttingsand permeates into the formation 33 on each side of the cut formed bythe abrasive cable.

FIG. 5 is a horizontal application of the concept of FIG. 3. FIG. 4depicts an impermeable subterranean basin structure formed in aformation such as rock by wax permeation from multiple closely spaceddirectionally drilled holes 34. The holes are first pre-heated bycirculating hot fluid through them. Molten wax is then circulatedthrough each of the directionally drilled holes for an extended period.The molten wax permeates the rock around the holes to form overlappingzones of wax-permeated soil.

FIG. 6 is a top-down variation on the concept of FIG. 4. FIG. 6 depictsa method of cutting a pathway downward between two substantiallyvertical holes 35. A pair of heavy pipes 36, supported by a suitabledrilling rig or crane are lowered into two adjacent holes. The tip ofeach pipe is equipped with a sprocket or pulley sheave 37 that guides anabrasive cable 38, such as a wire rope, chain or diamond wire saw, andcauses it to bear against the rock between said holes. Winches 39, or atraction drive system causes the abrasive cable to cut a pathway 40,through the formation rock. A flow of molten wax is injected through atleast one of the pipes such that molten wax flows through the cut toflush cuttings and transfer heat and permeate molten wax several inchesinto each side of the cut to increase the effective thickness of thebarrier as shown here in cross section plan view 41. After one verticalpanel is complete, the cutting apparatus is moved to the next section toform a continuous wall. Since the heavy pipe simply holds the pulleysheave and does not have to rotate, the winch system could also be builtinto a customized drilling rig wherein the abrasive cable runs insidethe pipe.

FIG. 7 depicts a method of drawing down the water table 42, in a porousformation to facilitate circulation of molten wax within a particularvertical interval of open borehole to heat the formation and permeate itwith molten wax. Water is extracted from the bottom of a well through atubing 43, while molten wax is injected through another tubing 44, whilebeing extracted from a point above this by a third tubing 45. Pressuremaintained in the borehole by the wax injection tubing helps depress thewater level to the bottom of the borehole while the pumping of the watercreates a cone of depression 46, to dewater the formation surroundingthe borehole. The dewatered formation heats more easily and the moltenwax permeates the heated zone 47.

FIG. 8 illustrates a series of boreholes wherein water is being pumpedfrom the bottom of every other borehole by a pumping means 48 creating acone of depression 49 of the water table around those odd numbered wells50. At the same time, a flow of heated matter such as hot water 51 iscirculated under pressure in the even numbered wells between 52. Aportion of the hot water that escapes through the fractures 53 from theeven numbered wells tends to follow the general pressure gradient flowto the odd numbered wells. This creates a thermal flow from evennumbered wells to odd numbered wells that carries heat to the evennumbered wells faster than it would without the removal of water fromthe odd numbered wells. The temperature increase in the recovered waterfrom the even numbered wells indicates the extent of the heating of therock between the wells. Steam or molten wax 54 may also be injected inthe annulus of the odd numbered wells to help heat the areas above thedepressed water table. When the temperature of the recovered water 55approaches the melting point of the wax, water circulation may bediscontinued and molten wax may be pumped down the annulus into the evennumbered wells. The molten wax will displace the water downward in thewells and also follow the pathways that the water has been using toreach the even numbered wells. Molten wax circulation will then beginfirst in the even wells and finally in the odd wells.

FIG. 8 also illustrates an alternate hole heating process in which onlyevery other hole, (the even numbered holes in a row of boreholes), isheated by electrical, heaters, heat transfer piping loops, or by directcirculation of hot water, steam, or molten wax through a tubing. As theeven numbered holes are heated, temperature probes are placed in the oddnumbered wellbores to measure the temperature by depth. The temperatureprobe is preferably a thermal imaging device that can measure thetemperature variation radially around the borehole continuously as it israised or lowered in the borehole. This allows it to see if thetemperature on one side of the borehole is lower than on the other sidefor the borehole. Such differences could be due to hole spacing, watercontent or variable formation materials. When the temperature of the oddnumbered, wellbores are at least equal or approach the melting point ofthe wax through the entire vertical interval, then it can be inferredthat the temperature of the formation between the wellbores has beenheated to at least this temperature. This helps assure that the moltenwax will be able to form a continuous path between adjacent wells. Theactual formation temperature at any point will increase nearer to theeven numbered wells. Temperature measurements or a thermal image of theborehole may indicate that the heating is following established patternsand provide sufficient evidence of uniform heating even before the oddnumbered holes approach the wax melting temperature. The infusion ofmolten wax and continued heating by circulation of molten wax into theeven numbered wells may preferably begin before the initial heatingmeans causes the odd numbered wells to reach or approach the wax meltingtemperature. The even numbered boreholes are called “primary” wellsbecause they could be drilled and heating begun before the secondarywells are drilled. The odd numbered or “secondary” boreholes would bethe ones drilled directly between the primary numbered or “secondary”boreholes would be the ones drill directly between the primary boreholesand would not be heated until after the temperature measurement profileindicated that heating progress from both adjacent primary boreholes wasnominal. Once the wax from the even numbered wells reaches the oddnumbered, secondary wells, hot wax recirculation would be started in theodd numbered wells too.

There are several variations on this approach but they all rely on usingheating means in the even numbered holes and monitoring the temperatureresponse in the odd numbered holes to know when enough heating has beendone. Since the actual spacing between wells, thermal conductivity, andthermal mass, at various depths may vary, this method monitors actualheating to verify that the formation is heated sufficiently for the waxto permeate.

Monitoring the temperature of the adjacent boreholes over time providesan indication of the identity of the thermal properties of the materialin the boreholes. It also indicates how the wax will flow and will serveas an indication of the thickness of the formed barrier or will predictthe heating parameters required to permeate the space between boreholescompletely.

FIG. 9 depicts the molten wax permeating radially outward through theheated zone 56 which overlaps between the wellbores. Vertical fracturessuch as this passing between the wellbores would be impossible to sealwith conventional grouts. However, the molten wax permeates and wicksthrough microscopic porosity that even water cannot readily penetrate.As the molten wax spreads from the wellbores through the heatedformation rock it reaches the fractures 57 between holes that do notcommunicate with the wellbores. Within the heated zone, the molten waxwill continue to seep into the fractures and begin to displace the waterfurther outward into the formation. The flow of molten wax into thesefractures is limited by the rate of permeation. Thus, the wax will cooland seal these fractures just outside the heated radius.

The desired pressure for adding the wax to the system is low. That is,the wax is delivered to the formation is equal to or less than thefracture gradient pressure of the formation. The fracture gradientpressure of the formation is the pressure that is needed for disruptingthe formation such as dislodging, breaking, or cutting material.

As shown in FIG. 10, the subterranean perimeter barrier wall 60 ispreferably made in hexagonal patterns 61 to minimize the length of wallfor the area enclosed. This technique is applicable to barriers madeusing the freeze walls or other grouting techniques, but is moreimportant for wax barriers because the wax material is much more costlyper unit volume than other grout materials. The wax barrier walls remainafter the recovery of the soil shale is complete and the hexagonalpattern of the barrier is more resistant to seismic damage than abarrier made in square sections. Since the vertical confining layer ofthe heated zones may be compromised it is important that the barriers bevery durable over time to prevent zones of differing pressure or groundwater quality from mixing.

FIG. 11 depicts a method of applying heated matter or molten wax to onlya portion of a borehole or damaged concrete pipe. Sealing means 64,located at each end of a pipe isolate an annular section of the boreholeoutside the diameter of the pipe. Flow lines 65 connected to theisolated annular space allow heated matter such as water or molten waxto be pumped into the space to bear against the borehole. Multiple ports66, and a floating piston 67, could be added to facilitate displacementof one fluid with another or with compressed air to empty the space.Molten wax flows into cracks and fractures 68 in the heated borehole.

After pre-grouting with such cement or clay based materials, thewellbore would be heated with electrical resistance heating elements, orby hot water injected through a tubing string to the bottom of thewellbore and circulated back to the surface or to a second tubing stringat a highest point in the wellbore where wax infusion is desired. Themolten wax is then pumped down the borehole from the annulus at the topof the well, while water is displaced up a tubing string, or smallerpipe. The wax which is lighter than water will remain as a separatephase above the water but will preferably be injected with enoughpressure to effectively displace the water downward in the borehole, orout into the formation. While formation water is free to move out intothe formation, as the wax moves outward into the formation it cools andsolidifies so its movement is thermally limited. Wax barriers may alsobe formed in saturated conditions by pumping molten wax down the annulusof the boreholes and displacing the water out into the formation or backto the surface through a tubing pipe extending to the bottom of thewellbore.

After the wellbore is full of molten wax, additional molten wax may becirculated in the well for an extended period to provide additionalheating as the wax permeates into the heated portion of the formation.This may be done by pumping hot wax down a tubing to the bottom of thewell and allowing it to circulate back to the top of the well where itis reclaimed, re-heated and re-injected. As the molten wax circulates inthe well, additional heat is transferred into the formation causing themolten wax zone to continue expanding radially outward. At the perimeterof the heated zone, the wax will revert to its solid form which is athermal insulator. This thermal insulation effect allows the heated zoneto expand to a greater diameter than would be possible with electricheating of the same net energy input. The pressure used to circulate themolten wax is preferably lower than the pressure needed to initiate newfractures in the formation being treated. One exception to this is todeliberately attempt to create vertical fractures that will tend to jointhe closely spaced boreholes. In this method an explosive perforatingmeans such as is known in the art of oil well technology may be used tocreate perforations oriented along the line of the closely spacedboreholes. The well may then be exposed to hydro-fracturing pressure, asis also well known in the art, to open vertical fractures which will aimin the general direction of the adjacent well. If several wells arehydrofractured at once it may be possible to open a continuous verticalfracture across many wells and inject a sand proppant into the crackusing a water gel designed to break after a few hours.

This method could be applied to sealing large boreholes, tunnels,concrete sewer lines or drilled shafts. At larger borehole diameters,the molten wax carries more heat for the surface area of the borehole sothe molten wax will penetrate further without pre-heating of theformation. This may be of particular use in sealing large drilled shaftsintended for long-term storage of nuclear wastes. The preferred waxwould be one that remains sticky and malleable at the undergroundtemperatures and can adapt to ground movement and seismic stress. Themolten wax would preferably permeate the first few meters of earthsurrounding the drilled shaft converting it into a waterproof and crackresistant material. In very large boreholes such as subway tunnels andshafts for storage of nuclear waste, the volume of molten wax requiredto flood the entire borehole may be excessive. A treatment pig or othermovable apparatus may be placed in the borehole to facilitate treating asection of the borehole with smaller volumes of wax. The pig wouldcomprise a pipe with means for sealing against the borehole on eitherside of the interval to be treated. The end seals may be mechanical,pneumatic or fluid filled. The pig apparatus may allow for directheating or circulation of heated matter within the interval to pre-heatthe formation wall. Molten wax may then be pumped into the interval topermeate and seal the borehole. Excess molten wax may then be pumped ordisplaced out of the interval while the apparatus is moved to the nextposition in the borehole. The apparatus may be pumped to a position orlowered vertically on drill tubing or wireline. In large horizontalshafts and tunnels the apparatus may be supported on wheels or tracksand moved mechanically when the seals are retracted.

A cracked concrete water or sewer line is essentially similar tofractured rock in a wellbore and may be repaired in a similar manner asa large tunnel. The line would first be heated by directing hot water orhot air through the line to heat it to at least the melting point of thewax. The molten wax would then be circulated through the line underenough pressure to overcome any external water pressure. The molten waxwould pass through any cracks into the cold soil and solidify into awaterproof solid patch. The wax would also preferentially flow aroundthe exterior of the heated pipe and produce a covering around the pipe.If only a limited area of the pipe requires repair, the apparatusdescribed above could be positioned in that area to heat the section ofpipe and apply the molten wax.

The present invention has many environmental applications in addition tofacilitating recovery of oil from oil shale. These include coal bed,oil, tar sands, or oil shale recovery operations. In the oil shaleapplication, the invention places a barrier made from wax around theperimeter of the heated oil shale area. The barrier may preferably beformed far enough from the area being heated that it is notsignificantly affected by the oil shale heating process. However, ifneeded, chilling means, such as pipe loops carrying chilled liquidammonia solution, may be placed in the boreholes while they are stillliquid but after the barrier is in place to prevent heat from the oilshale operation from liquefying the wax barrier. When the oil is fullyextracted and the heat subsides, the chilling may be turned off and thewax will maintain the barrier in perpetuity without any further energyinput or maintenance.

After wax treatment of a borehole is complete, the molten wax in theborehole may be displaced back to the surface by grout or water andreclaimed. The open hole may be left full of air or water and also maybe equipped with sensors for leak detection. If the wax is displacedback to the surface with air or nitrogen gas the absence of water inflowwill provide some evidence that at least the wellbore has been sealed.Leaks between adjacent boreholes due to insufficient wax permeation maybe identified by temperature differential or by electrical conductivityacross the barrier. The wax permeated rock will have a much lowerelectrical conductivity so a borehole outside the perimeter and insidethe perimeter could be used to make a measurement.

Leaks may be identified with some precision by temperature measurementsafter the water table within the perimeter is drawn down prior to oilshale heating. Leaks in the barrier will allow cold formation water tocross the barrier. Substantial flows will cause a local temperature dropover time that can be detected by temperature sensors in the wells. Evenbefore the main heating begins, water inflow will be colder than theambient temperature of the heated rock which surrounds wells that havejust received wax infusion. Vertical intervals where the wellbore is notas hot as other places may indicate an insufficiently heated area or anarea that did not receive enough wax. It may even be possible to performan infrared thermal survey of the wellbore indicate if there is moreheat in the direction of the barrier than perpendicular to the barrier.The wellbore surface closest to the adjacent wellbore should cool moreslowly than the portion away from the line of the barrier. A temperatureprofile by depth of the well should be sufficient to indicate areaswhere leaks may exist. Such potential leaks could be repaired bycirculating additional molten wax in the well for an extended period ofmonths.

Wax Identity

Wax is a waterproof substance that is a solid or plastic semisolid atambient temperature and that, on being subjected to slightly highertemperatures, becomes a low viscosity liquid. The chemical compositionof waxes is complex; all of the products have relatively wide molecularweight profiles, with the functionality ranging from products, whichcontain mainly normal alkanes to those which are mixtures ofhydrocarbons and reactive functional species. Common waxes includerefined paraffin, slack wax, petrolatum, crude petrolatum,microcrystalline wax, polyethylene, alpha olefin, plant derived wax,coal derived wax, and wax refined from solid hydrocarbon deposits suchas oil shale. Acceptable waxes include WAXFIX 123™, WAXFIX 125™, WAXFIX145™, and WAXFIX 166™, which are commercially available products fromM-I L.L.C. of Houston, Tex. and are proprietary wax blends with nominalmelting points of 123 F, 125 F, 145 F, and 166 F, respectively. MoltenWAXFIX products are 15 to 20 percent lighter than water. WAXFIX productsinclude surfactants and wetting agents that comprise less than onepercent of the total mass.

The wax to be used in subterranean barrier work is selected based onlocal availability and cost as well as physical properties. Any type ofnatural or manmade thermoplastic may be used in the process if itsproperties are suitable. Branched chain wax such as crude petrolatum maybe preferred for its resistance to biological attack and its resistanceto cracking. Straight chain waxes such as paraffin may be preferred forlow viscosity and lower melting point. Synthetic wax such as alphaolefin may be utilized as well. Branched chain or microcrystalline waxesare preferred for their higher melt temperature that may allow them tobe used at greater depth. Various types of wax may be blended to achieveideal properties. Blends of materials that are only partially refinedsuch as slack wax with crude petrolatum are generally lower in cost andwork as well.

Adding a surfactant to the wax is desirable to maximize permeation andimprove wax wetting of soil and rock that contains water. When formingbarriers below the water table, hot air injection as described above maybe useful for driving water from the formation. Heating the formationand its water above the melting point of the wax will allowemulsification of the water as droplets of water inside a molten waxliquid phase. If the water droplets within this emulsion aresufficiently small, the emulsion can penetrate the formation. As theformation becomes wetted with molten wax, additional penetration will bepossible and less water will flow into the borehole. Surfactantmaterials that function only at the temperatures of molten wax arepreferred since it is desired that the final condition of the formationbe impermeable to both water and oil. Conventional dewatering of thewells prior to and during the pre-heating process may be desirable tomaximize penetration into the formation. The preferred method is todrive as much water from the formation as possible and then usesurfactant modified wax to help displace the water and oil wet theformation. If the formation is fully saturated with water and quitepermeable to water, injection of the molten wax under pressure into theupper portion of the pre-heated and water-filled borehole, allows themolten wax, which is lighter than water, to form distinct interfaceabove the water, as the pressurized hydrostatic head of wax displacesthe water column downward and outward into the porosity of theformation.

Additional information regarding suitable waxes may be obtained withinU.S. Pat. No. 6,860,936, which is incorporated by reference in itsentirety.

The foregoing description of preferred and other embodiments is notintended to limit or restrict the scope or applicability of theinventive concepts conceived of by the Applicant. In exchange fordisclosing the inventive concepts contained herein, the Applicantdesires all patent rights afforded by the appended claims. Therefore, itis intended that the disclosed methods include all modifications andalterations to the full extent that they come within the scope of thefollowing claims or the equivalents thereof.

1. A method of infusing molten wax into a desired volume of asubterranean formation to make said desired volume substantiallyimpermeable comprising: forming at least one pathway from the surface toat least one point in the desired volume of the subterranean formation;heating said desired volume of the subterranean formation to atemperature above the melting point of the molten wax; and injecting amaterial consisting essentially of molten wax into the pathway, whereinthe wax flows into and permeates the formation pores and microporeswithin the desired volume; wherein the molten wax subsequently hardensand renders said desired volume substantially impermeable.
 2. The methodof claim 1, wherein the desired volume comprises a plurality ofboreholes and the space between and around the boreholes.
 3. The methodof claim 2, wherein the injecting step further comprises providing ahydrostatic head of molten wax to at least a portion of at least one ofthe plurality of boreholes, wherein the molten wax flows into and fillsformation porosity between the boreholes to substantially form ahydraulic barrier between and around the boreholes.
 4. The method ofclaim 2, further comprising cutting a sawed pathway between adjacentboreholes.
 5. The method of claim 4, further comprising circulatingmolten wax through the adjacent boreholes and the sawed pathway.
 6. Themethod of claim 5, wherein the face of the sawed pathway is heated bythe flow of the molten wax.
 7. The method of claim 5, wherein thecirculating molten wax transports cuttings to the surface and whereinthe circulating molten wax is filtered, re-heated, and re-injected. 8.The method of claim 5, wherein the molten wax permeates into the face ofthe sawed pathway to substantially form a hydraulic barrier around thesawed pathway and between the adjacent boreholes.
 9. The method of claim2, wherein the heat is provided by injecting hot fluids into theborehole, circulating hot fluids or gas within the borehole, placing anelectrical heating device into the borehole, providing molten wax at atemperature sufficient to heat the formation, or introducing reactantsinto the borehole to facilitate an exothermic chemical reaction.
 10. Themethod of claim 1, wherein the subterranean formation is saturated withwater and wherein the step of injecting molten wax into the pathwaycomprises applying pressure to the wax.
 11. A method of infusing moltenwax into a desired volume of a subterranean formation to make saiddesired volume substantially impermeable comprising: forming at leastone pathway from the surface to at least one point in the desired volumeof the subterranean formation, wherein the at least one pathway forms asubstantially vertical barrier within an oil shale formation stratacomprising walls forming joined hexagonal cells; heating said desiredvolume of the subterranean formation to a temperature above the meltingpoint of the molten wax; and injecting molten wax into the pathway,wherein the wax flows into and permeates the formation pores andmicropores within the desired volume; wherein the molten waxsubsequently hardens and renders said desired volume substantiallyimpermeable.
 12. A method of strengthening and waterproofing a hole in asubterranean formation by infusing a material consisting essentially ofwax into the porosity of the surrounding subterranean formation to adesired distance comprising: heating at least a portion of the walls ofthe hole above the melting point of the wax; applying a hydrostatic headof the wax to the heated area, wherein the wax permeates into theporosity of the surrounding subterranean formation for the desireddistance; and wherein the wax displaces water into the formation as thewax permeates into the porosity of the surrounding subterraneanformation to strengthen and waterproof the area surrounding the hole.13. The method of claim 12, wherein the hole is a tunnel, shaft,wellbore, or pipeline.
 14. The method of claim 12, further comprisingmixing an additive with the wax to facilitate displacement of water andenhance permeation.
 15. The method of claim 14, wherein the additive isa surfactant.
 16. The method of claim 12, wherein said method furthercomprises removing excess molten wax remaining within the hole.
 17. Amethod of forming a barrier within a subterranean formation laterallyalong a desired boundary defined by a plurality of drilled boreholes andextending along at least a portion of the length of the boreholes,comprising: heating the subterranean formation between at least two ofthe plurality of boreholes to a temperature above the melting point of awax; and injecting a material consisting essentially of molten wax intoat least one of the at least two boreholes, wherein the wax flows intothe porosity of the heated subterranean formation along the desiredboundary; wherein the wax displaces fluid and gas within the porosityand cools to form a substantially impermeable subterranean barrier. 18.The method of claim 17, wherein heat in the heating step is provided byinjecting hot fluids or gas into the borehole, circulating hot fluidswithin the borehole, placing an electrical heating device into theborehole, providing molten wax at a temperature sufficient to heat theformation, or introducing reactants into the borehole to facilitate anexothermic chemical reaction.
 19. A method of forming a barrier within asubterranean formation along a desired boundary defined by a pluralityof drilled boreholes and extending along at least a portion of thelength of the boreholes, comprising: heating the subterranean formationbetween at least two of the plurality of boreholes to a temperatureabove the melting point of a wax; and injecting the wax into at leastone of the at least two boreholes, wherein the wax flows into theporosity of the heated subterranean formation along the desiredboundary; wherein the wax displaces fluid and gas within the porosityand cools to form a substantially impermeable subterranean barrier,wherein the desired boundary surrounds an oil shale formation, andwherein the barrier substantially encloses a desired portion of the oilshale formation.
 20. The method of claim 19, wherein the barrierprotects ground water from contamination by the production ofhydrocarbons from the oil shale formation.
 21. A method for constructinga barrier within a subterranean formation, comprising: providing heatingmeans for heating the formation adjacent to the desired extent of thebarrier; delivering a hydrostatic head of a material consistingessentially of molten wax to at least a portion of the heated formation;allowing the molten wax to flow into and permeate voids and micron-sizedporosity of the heated formation; and allowing the wax to cool andsolidify to create the barrier.
 22. The method of claim 21, furthercomprising verifying the integrity of the barrier.
 23. The method ofclaim 21, further comprising repairing defects in the barrier.
 24. Themethod of claim 21, wherein the barrier is a continuous barrier greaterthan one thousand feet deep.
 25. The method of claim 21, wherein thebarrier is formed between: a) adjacent vertical drilled bore holes; b) aseries of angled pathway holes tracing out a barrier pathway; or c) aseries of directionally drilled bore holes tracing a basin shape. 26.The method of claim 21, wherein the barrier is formed between: a) adirectionally drilled horizontal bore hole and the surface, along asawed pathway; or b) two adjacent bore holes along a sawed pathway. 27.A method for constructing a barrier within a subterranean formation,comprising: providing heating means for heating the formation adjacentto the desired extent of the barrier; delivering a hydrostatic head ofmolten wax to at least a portion of the heated formation; allowing themolten wax to flow into and permeate voids and micron-sized porosity ofthe heated formation; and allowing the wax to cool and solidify tocreate the barrier wherein the barrier surrounds a formation containingoil shale.
 28. The method of claim 27, wherein the barrier protectswater aquifers from contamination by the production of hydrocarbons fromthe oil shale formation.